1. Field of the Invention
The present invention relates generally to freeze drying apparatus, and more particularly, this invention relates to an improved condensation chamber for freeze drying apparatus.
2. Description of the Prior Art
The method of freeze drying biological specimens and other materials such as coffee and other food products by sublimation of ice in a vacuum has been known for over 50 years. It was not until shortly before World War II, however, that the true commercial potential of laboratory freeze dryers and the process of sublimation were recognized. Particularly, during World War II, substantial development was made in the equipment and techniques for the purposes of supplying medical products to the armed forces. Since that time, increased interest by food processors as well as pharmaceutical manufacturers has resulted in further development of freeze drying equipment. Thus, freeze drying has found application not only in the laboratory for various scientific purposes, but commercially as well.
Basically, the process of freeze drying involves the lowering of the temperature of a moisture-containing item or sample until it is in a completely solid state, i.e., until it is frozen. The sample is then maintained in the area of a very low absolute pressure or high vacuum and subjected to a controlled heat input. Application of the heat to the product at a controlled rate results in the water content of the frozen sample being sublimated (i.e., converted directly from a solid to a gas without passing through the liquid state). The gaseous water vapor is then evacuated from the drying chamber and refrozen in a refrigerated condensation chamber thereby protecting the vacuum pump oil from contamination by the water vapor. The refrozen moisture can be removed from the condensation chamber when the chamber is filled.
Various types of freeze drying equipment are well known in the art as exemplified by the apparatus disclosed in U.S. Pat. Nos. 3,950,963-Sutherland and 3,795,986-Sutherland et al., both of which are assigned to the same assignee as the present invention. Since the capabilities of such freeze drying equipment are dependent upon the amount of moisture that may be removed from the moisture-containing item being dried, it is desirable to maximize the moisture-removing capabilities of the equipment. The moisture-removing capabilities of the equipment are to a great extent determined by the capabilities of the condensation chamber to condense and freeze the moisture removed from the item. Thus, it is a desirable advance in the art to maximize the capabilities of the condensation chamber in freeze drying equipment so that the maximum available volume of the condensation chamber is utilized to refreeze the sublimated moisture.